The broad, long term of this proposal is to gain an understanding of the mechanism(s) of recurrent otitis media with effusion (OME) due to nontypable Haemophilus influenzae (NTHI). The four specific aims of the project are: 1) Characterize the pattern of nasopharyngeal (NP) carriage of NTHI from birth to one year of age in otitis prone (OP) and nonotitis prone (NOP) children. 2) Identify the host factors that are associated with NP carriage of NTHI. 3) Critically examine the immune response to NTHI among individuals with two or more documented episodes of OME due to different strains of NTHI. 4) Determine the IgG subclasses of antibody that are responsible for the bactericidal activity to NTHI. The first two specific aims will be addressed in a prospective longitudinal study of children who will be followed from birth through the age of two years. The NP carriage of NTHI will be monitored and related tot he incidence of OME. NTHI strains will be characterized by the pattern of outer membrane proteins (OMP) to distinguish newly acquired strains from older strains. Environmental and host factors that affect carriage will be assessed. For example, the ability of respiratory tract epithelium to permit NTHI adherence will be determined by in vitro studies with buccal epithelial cells from OP and NOP children. Differences in the local immune response to NTHI will be characterized by measuring the NTHI specific IgG, M, A and secretory A in NP secretions with an immunodot assay. The second two specific aims will be addressed by studying clinical specimens obtained during the original grant. Acute and convalescent sera from children will be examined for strain specific as well as cross reacting bactericidal antibody. The presence of and bactericidal activity of IGG antibody to specific OMPs, in particular P6/PAL, will be evaluated by Western blot and immunodot analysis. The IgG subclasses of antiNTHI antibody responsible for bactericidal antibody will be determined in meddle ear fluid and serum by ELISA methodology. A better understanding of the immune response to NTHI will hasten the development of an effective vaccine.